Field of the Invention
The present invention relates to an exhaust gas analysis system to be mounted on a mobile object, such as a vehicle. The exhaust gas analysis system collects part or all of an exhaust gas discharged from an internal combustion engine of the mobile object, and dilutes and analyzes the exhaust gas.
Description of the Related Art
A conventional exhaust gas analysis system mounted on a vehicle, is configured as described in WO 2010/007965. In this configuration, part of the exhaust gas discharged from the internal combustion engine is separately collected through an exhaust gas introduction pipe and introduced into a micro-tunnel (diluter). The collected exhaust gas is diluted with a diluent gas, and the diluted exhaust gas thus obtained is then introduced into an analyzer, such as a PM collection filter.
In the exhaust gas analysis system, a diluent gas flow rate regulation mechanism and a diluent gas flow rate measurement mechanism are disposed on the diluent gas introduction pipe connected to the micro-tunnel. A diluted exhaust gas flow rate regulation mechanism and a diluted exhaust gas flow rate measurement mechanism are disposed on a flow channel on a downstream side of the micro-tunnel. And, a differential pressure flowmeter, such as a Venturi flowmeter, is used for the diluent gas flow rate measurement mechanism and the diluted exhaust gas flow rate measurement mechanism.
The exhaust gas analysis system is configured to perform a partial-flow dilution control on the basis of a flow rate of the exhaust gas discharged from the internal combustion engine, by controlling the diluent gas flow rate regulation mechanism and the diluted exhaust gas flow rate regulation mechanism. That is, a flow rate of the diluent gas introduced into the micro-tunnel is regulated so as to stabilize a ratio (split ratio) of the flow rate of the exhaust gas discharged from the internal combustion engine and the flow rate of the exhaust gas separately collected into the exhaust gas introduction pipe.
However, in the exhaust gas analysis system mounted on the vehicle, acceleration can act on the exhaust gas analysis system, depending on operation situations, such as an acceleration operation, deceleration operation, or coasting operation of the vehicle, or road situations, such as road surface irregularities. Consequently, a measurement error caused by an influence of acceleration can occur on a differential pressure gauge of the diluent gas flow rate measurement mechanism (differential pressure flowmeter) and on a differential pressure gauge of the diluted exhaust gas flow rate measurement mechanism (differential pressure flowmeter). Here, the differential pressure gauge used for flow rate measurement handles micro pressures and hence is significantly affected by the acceleration. Therefore, the influence thereof differs depending on a direction in which the acceleration acts.
Particularly, in a system in which the flow rate of the exhaust gas, to be separately collected into the exhaust gas introduction pipe, is controlled to be a difference between the diluted exhaust gas flow rate and the diluent gas flow rate (“sample flow rate”=“diluted exhaust gas flow rate”−“diluent gas flow rate”), a control error of the sample flow rate may increase due to a measurement error of the diluted exhaust gas flow rate and a measurement error of the diluent gas flow rate.